Then may be somethink like:
*A 40 pin dip derivate (easier to solder in many times)
*MAX232 or equivalent + DB9 serial For "serial ISP" and communications
*DB25 For easy "parallel ISP"
*External RAM and ROM as Craig says for experimenting and doubts fixing
*Some leds with its buffers and dip switches to simulate inputs an outs but not fixed to a pin, a pin and a jumper cable will be better
*LCD interface -Memory mapped and/or "port mapped"
*the 8 pin sil port to alow a 4x4 kbd or a cable configuration of leds / switches
*The ps2 keyboard interface
*The reset and prog pushbutons
*The voltage supervisor
*The 5V source without the transformer (for the WW compatibility)
*Some memory maped IO?
*Serial busses SPI and I²C-- By soft or by hard?